Trouble with the fish

19 February 2008

We have been having terrible trouble with our aquaponics system and the fish have been dying. About two weeks ago we noticed the water going a revolting shade of pea green. The fish were fine but something was happening with the water. When it started getting worse, we changed the water. We put the fish back into the clean water, the next day is was brown.

Our aquaponics system is made up of two grow beds that sit above a 3000 litre fish tank. One of the grow beds was cleaned out recently and replanted. When the water didn't improve, we changed it again. Luckily it's been raining a lot, and as we use only rain water in our system, we had the tanks replenished every night.

But replacing the water didn't improve the situation, so we ripped out all the plants and cleaned the second grow bed. It was full of green slime, roots and duck weed. This is an all day job that involved shovelling out the gravel, washing it in a sieve, placing it in the wheelbarrow and buckets, cleaning out the galvanised container and shovelling it all back in again.

When we did that, there still wasn't much of an improvement so we changed the water again and waited. Overall, the water was changed three times and it's been every colour from bright green to a mid brown.

Every day a few fish died. It was horrible. I felt really bad that we had these fish and we didn't know enough to keep them alive and healthy. We did a lot of reading and realised the increased temperature and the afternoon summer sun on the water caused an algal bloom. The algae consumed a lot of the dissolved oxygen, and that is what made the fish sick. They didn't have enough oxygen, even though we had four bubblers running all the time and water was falling from the grow beds that created more bubbles.

We now have a cover over the water to protect it and the fish from the sun. They like living in dark water so I think they're happier than they were when it was unprotected. Over the past two weeks we've gone from about 80 fish to around 50. Yesterday was the first day we had no fatalities. I think the balance has been restored. We've lost a few of the larger fish we were hoping to eat fairly soon. The largest of the fish that died was about 22cm (8½ inches).

So now we're starting from scratch again. We'll have to replant the grow beds and wait until the beneficial bacteria in the gravel starts growing again. Luckily it has been kick started with a couple of buckets of unwashed gravel. The bacteria converts the fish waste into nutrients for the plants.

My hope is that the fish remain healthy and we repeat the success with the plants that we had last year. The brandywine tomatoes we grew in the system last year were the best tomatoes I've even eaten - they were sweet and juicy and had that old-fashioned flavour of real tomato.

It's still too dark to see anything outside but if, when I go out, I find the fish well, I think we'll be over this horror session. This lesson has taught me there is still a lot to learn about aquaponics but I hope we can continue learning and provide a clean and healthy environment for our fish.

11 comments

Hi Rhonda Jean :) I've been doing my Monday catch up reading - it's such a treat to read you and visit a little!

This post is so interesting - thanks for sharing even your challenges. I am keeping a list of ideas from your aquaponics and gardening and many other project areas for when my sweeties are a little older. You have given us some wonderful ideas!

Hope that you have a lovely week, and that the fish are well ;) Love, Q

I'm sure that would have been quite distressing for you ~ particularly because you didn't know why. I'm glad the situation is sorted out and that your fish are happy again.

I love the photo of your rhubarb. I have some growing but it doesn't look nice and red like you see in the shops. Mine has very thick stems and is very green. It's been there for about a year but didn't really take off til a couple of months ago. I'm starting to wonder if there's more than one variety of rhubarb.

That's good to hear that the fish are ok this morning! You must be relieved to have figured out what the problem was and able to rectify it. The only fishing going on around here is ice fishing and to be frank, I don't think I'd feel comfortable being out on the ice this year -- too many accidents of people falling through the ice. I think i'll wait until the summer months and go fishing the old fashion way -- sitting in a boat with a good book and your rod in the water :)

EEeeeewww... sound like a bad case of what we call in the USA, "Red Algae". We lived in a small town for a while years ago. Their water reservoir/tanks were suddenly hit with that same kind of algae. One morning we turned on the faucet to our shower and brownish-red water came out!! Yuck! I called the city utility office and the lady said in a thick southern accent, "It's perfectly safe to drink." Yeah, right! I don't think so... Somehow the thought of making my morning juice with that scuzz wasn't the most appetizing thought. I was certain my spoon would have dissolved in that water - or maybe I'd have four hundred kidney stones by Lunchtime. LOL! We bought bottled water until a nearby university could figure out and solve their problem.

So sorry about the fish! But it sounds as if you are on the right track.Admiringly,HeatherJ

So glad to hear that the fish are OK and that you have cracked the problem. Would a reflective surface help? If so, some old windscreen reflectors might do the trick, in the UK and here you can usually find places selling them really cheaply.

I'm looking at 'velcroing' some as curtains on the side windows of my car for summer (when parked) to try and reduce the internal temperature.

Rhonda,This post hits too close to home. As for my thesis work, it's the dissolved nutrients in the water that is causing eutrophication in the aquaponics water. The nutrients (phosphates) stimulate the algal blooms which depletes the oxygen level in the water and as you mentioned gets worse as the temp rises. :)Environmentally, where I live in the U.S., there is an ongoing court battle between two states regarding the degradation (eutrophication) of a local scenic river. Some think this is due to phosphorus runoff from years of applying broiler litter as an organic fertilizer to farm land upstream as a means of disposal.

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